We examine the relation between surface brightness , velocity dispersion and size - the fundamental plane - for quiescent galaxies at intermediate redshifts in the COSMOS field .
The COSMOS sample consists of \sim 150 massive quiescent galaxies with an average velocity dispersion \sigma \sim 250 km s ^ { -1 } and redshifts between 0.2 < z < 0.8 .
More than half of the galaxies in the sample are compact .
The COSMOS galaxies exhibit a tight relation ( \sim 0.1 dex scatter ) between surface brightness , velocity dispersion and size .
At a fixed combination of velocity dispersion and size , the COSMOS galaxies are brighter than galaxies in the local universe .
These surface brightness offsets are correlated with the rest-frame g - z color and D _ { n } 4000 index ; bluer galaxies and those with smaller D _ { n } 4000 indices have larger offsets .
Stellar population synthesis models indicate that the massive COSMOS galaxies are younger and therefore brighter than similarly massive quiescent galaxies in the local universe .
Passive evolution alone brings the massive compact quiescent COSMOS galaxies onto the local fundamental plane at z = 0 .
Therefore , evolution in size or velocity dispersion for massive compact quiescent galaxies since z \sim 1 is constrained by the small scatter observed in the fundamental plane .
We conclude that massive compact quiescent galaxies at z \lesssim 1 are not a special class of objects but rather the tail of the mass and size distribution of the normal quiescent galaxy population .